The High-Definition Multimedia Interface (HDMI) is an audio/video data interface suitable for transmitting uncompressed digital data and typically connects audio/video devices such as Camcorders, BluRay and DVD players to other devices such as TVs, and PC monitors. The HDMI specification defines all aspects of the standard such as protocols, signals, electrical interfaces and mechanical requirements. Version 1.4 of the HDMI standard further includes a specification for an automotive connection system which can be used for connecting Audio Visual devices such as DVD players, Blu-Ray video players, and mobile applications to video screens and other vehicle systems using HDMI cabling built into the vehicle.
The HDMI interface has several different groups of transmission lines operating at different frequencies. One group of lines are the very high speed serial lines which use a Transition Minimized Differential Signalling (TMDS) technique originally developed for the digital visual interface (DVI) which can be used to transmit signals up to frequencies of several Gigabits per second. TMDS lines are current-driven lines terminated at the HDMI receiver. A second group is the +5V and HPD lines, used for EDID power and feedback to enable RX detection which are continuous voltage lines. DDC lines which support an I2C interface. A CEC line which is a consumer interface ultra low speed line. A HEAC overlayer used to transmit AC signals on the HPD and unused utility lines which can be used for example to provide an Ethernet and SPDIF interface.
For an Automotive implementation of HDMI systems, an abnormal short circuit may occur to voltage sources in the car which can for example be 12 Volts, 18 Volts, 24 Volts or higher. However, HDMI interfaces are not designed to tolerate such voltage levels on very high speed serial lines which use a Transition Minimized Differential Signalling (TMDS) technique. TMDS lines on HDMI interfaces may be protected from large transient voltages using an ESD protection device such as the NXP PESD1LVDS IC. However, this will not protect the TMDS lines from a permanent short circuit to a DC voltage source.
This problem may also occur when HDMI systems are used in aircraft to communicate audio and/or video data between devices.